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How do I read the cloud drift wind data?


What are cloud drift winds?

Geostationary satellites track winds in the upper atmosphere by observing the movement of image features in time. The distance traveled by a feature in the time between images is the speed. The height of the feature is often determined from its temperature. We reference features, because while clouds are easy to track by our eyes, features in water vapor imagery are easier to track with a computer and provide information on upper level winds in the absence of clouds. Examples of operational cloud drift winds are available on the NESDIS website.

How do I access NCDC-archived cloud drift wind files?

What is the format of the NCDC-archived cloud drift wind files?

Data are stored in flat-binary files. Data records contain information for one wind observation and the number of records per file is deduced from the file size. A record is 200 bytes which consists of 18 4-byte integers containing data followed by 32 4-byte integers containing zeros. The following table describes the data within the first 18 integers.

The information in this table is provided as guidance and is not to be considered the final documentation of the data. This was derived from page 165 of the GOES Satellite Derived Winds Processing System (HD WINDS) Programmer Maintenance Manual.
Offset Description Units Scale
0 Date of observation YYYYMMDD 1
1 Time of observation HHMM (UTC) 1
2 Date created YYYYMMDD 1
3 Time created HHMM (UTC) 1
4 Pressure Level of the Obs. mb 10
5 Temperature Kelvin 1
6 Latitude Degrees North 100
7 Longitude Degrees West 100
8 Wind Direction Degrees East of North 1
9 Wind Speed meters / second 10
10 Unknown
11 Unknown
12 Unkown
13 Unknown
14 Unknown
15 Unknown
16 Unknown
17 Unknown
To convert the integer value to the actual value, divide by the scale. An IDL routine is also available which will read the data.